1. FIELD OF THE INVENTION
The present invention relates to the generation of shock waves by impact apparatus and more particularly, but not by way of limitation, to an Isentropic Compressive Energy impact disk or pillow for interpositioning between an impactor member and a target specimen for controlling the shock wave rise times and including a method of manufacturing said pillows by a particle sedimentation process.
2. HISTORY OF THE PRIOR ART
Shock wave techniques are used for a number of purposes in today's technology. The information they provide on the behavior of materials at very high pressures and deformation rates has useful applications in such fields as seismology, mining, and weapons technology. Shock waves are also used to synthesize industrial diamonds and boron nitride, and they can impart unique chemical properties to certain materials, increasing their catalytic activity by several orders of magnitude. Shock waves provide the only way to measure material properties at the ultra-high pressures which exists in the interiors of large bodies such as planets. Additional uses for shock waves are still being discovered.
One of the methods for creating high-pressure shock waves is to impact the target with a projectile which has been accelerated to a high velocity by a specially designed gun. It is generally desirable to use the impact to create motion in a single direction in as large a region of the target as possible, because the simplicity of such motion makes it more mathematically tractable and hence leads to better determinations of the properties of the target specimen. In order to obtain one-dimensional motion, the impact surfaces of the target and the projectile nose are made flat, and the impact takes place in a vacuum.
Such flat plate impacts cause shocks with almost instantaneous rise-times to be generated in both the target and the projectile nose-piece. The shock propagating through the target compresses it and raises its temperature. Because of the dissipative effects associated with the very sudden jump in pressure, the temperature increase can be thousands of degrees if the shock pressure is sufficiently high. The experimenter has little control over the rise time of the shock and the temperature behind the shock front, i.e., the entropy increase, in these traditional experiments.
In order to prevent most of the entropy increase associated with impact testing, some experiments have achieved quasi-isentropic waves by using a ring-up effect in liquid hydrogen, by using several layers of different materials to break up the shock, or by magnetic compression.
In the former two cases, a large shock is replaced by a number of smaller component shocks. Although this prevents most of the entropy increase of the single large shock, the strain rate in the overall wave profile is not well defined because it is very high in any one of the small shock components, and almost zero during the brief interval between any two small shock components. This decreases the usefulness of these waves in many cases where the material properties of concern are functions of the strain rate.
The magnetic compression experiments produce cylindrical (two dimensional) compression of the specimen instead of linear, one dimensional, compression. Such experiments have suffered from difficulties in accurately measuring the pressure and volume reached during the compression.